In the fields of biology, chemistry, and medical care, the so-called dispensing device is used to dispense a liquid sample and a liquid reagent into containers, such as test tubes or a microplate, in units of very small amounts for the purpose of analysis and inspection. That dispensing device receives attention particularly in use of dispensing a large number of samples, reagents, etc. for analysis of genetic information of animals and plants, screening in creation of medicines, and examination of specimens, e.g., bloods and viruses, in medical care. The reason is that the dispensing device can quickly and accurately perform a lot of operations, which are difficult for a person to manually perform using a pipette, for example. Because the dispensing is performed in many uses as described above, a discharge amount of one droplet is required to be very small (e.g., order of μL (micro-liter) to nL (nano-liter)) and the dispensing device is also required to discharge a very small amount of liquid with high accuracy in order to effectively utilize the samples that are generally expensive or rare. Further, various kinds of analysis and inspections are often performed together from the viewpoint of efficiently progressing a lot of operations. To that end, it is also required for one dispensing device to discharge plural types of liquids.
In general, the dispensing device mainly includes a discharge unit constituted by, e.g., a pump for extracting, from a container storing a liquid sample or a liquid reagent, the sample or the reagent, a nozzle through which the extracted sample or reagent is discharged, and pipes for interconnecting the pump and the nozzle, a driving unit serving as a mechanism to relatively move the nozzle and a container as a dispensing target, and a control unit for controlling operations of individual components including the pump, the driving unit, etc. Among those units, an especially important one is the discharge unit that directly handles the liquid sample and the liquid reagent.
Although there are various types of discharge units, they are mainly grouped into two types depending on a direction in which the sample or the reagent is supplied. In one type, the sample or the reagent is supplied from an opposite end to a discharge port (nozzle). In the other type, the sample or the reagent is supplied from the same end as the discharge port (nozzle), i.e., the sample or the reagent is sucked through the discharge port (nozzle) and then discharged through the discharge port (nozzle). In particular, when the sample or the reagent is expensive or rare and can be prepared just in such a small amount that the pump, the pipes, etc. cannot be filled with the sample or the reagent in amount necessary for operations, or when there are many types of samples or reagents to be discharged and operations of removing the samples or the reagents filled into the pump, the pipes, etc. and cleaning them are troublesome, the other type of the dispensing device is often used in which the sample or the reagent is supplied from the same end as the discharge port (nozzle), i.e., the sample or the reagent is sucked through the discharge port (nozzle) and then discharged through the discharge port (nozzle).
In the dispensing device of the other type described above, for accurate discharge in a very small amount, the sample or the reagent discharged through the discharge port (nozzle) is often discharged in such a manner that the sample or the reagent is departed from a tip end of the discharge port (nozzle) before reaching a target, thus causing the sample or the reagent to fly toward the target. In this specification, such discharge is called “fly-discharge” or “non-contact discharge”.
Patent Document 1 states that a dispensing device for discharging a liquid with reciprocal motions of a piston has a problem of being not suitable for a dispensing operation, which requires accuracy of less than several μL, due to the occurrence of a dispensing error. To cope with such a problem, Patent Document 1 proposes a dispensing device in which a liquid can be discharged in an amount of about 200 μL at certain accuracy by discharging the liquid with application of positive pressure from a pressurized gas supply source (or application of positive pressure from a cylinder device in a combined manner). In the device of Patent Document 1, however, because gas (air) is used as a pressure transmission medium, a problem may arise in response and accuracy due to compressibility of the gas (air). For that reason, a dispensing device using a liquid as a pressure transmission medium is also proposed as disclosed in Patent Document 2. Among dispensing devices each using a liquid as a pressure transmission medium, there are dispensing devices, as disclosed in Patent Documents 3 and 4, in which, instead of directly discharging the sample or the reagent with the action of a piston (plunger) of a pump, a valve is disposed midway a piping line and the sample or the reagent is discharged with opening and closing of the valve while the sample or the reagent is previously pressurized by the pump or another pressurizing means.